• Optical dual-level sensing — one sensor body carries two detection points, an ATO level sensor below and a fail-safe sensor above, so an overfill has to defeat two separate readings.
• QST over-run protection — the controller learns how long your first refill takes and alarms if a later refill runs six times longer. AutoAqua's worked example: a 10-second normal fill alarms at 60 seconds.
• Audible and visual alert — the Duo's manual specifies an audible and visual alarm, and a touch button silences it.
• Catches more than a stuck float — QST detects an empty reservoir, a failed sensor and a failed pump, not just a jammed switch.
• 180 cm sensor lead — 60 cm longer than the Smart ATO Lite, which matters when the controller is mounted outside a cabinet.
• Magnet mounted, no drilling — sensor and tube holder each clamp through glass or acrylic up to 12.7 mm.

AutoAqua publishes no rated aquarium volume and no noise figure for the Duo. Those rows are absent rather than estimated.

This is the original Smart ATO Duo, model SATO-280P, identified by barcode 4714041211825. AutoAqua's current catalogue lists a second-generation Duo, the SATO-286P, in its place.

The pump specification is unchanged between the two: 280 L/h and 250 cm of head either way. When ordering a replacement pump or sensor later, quote SATO-280P rather than the G2 code.

• Smart ATO Duo controller with dual optical sensor
• Universal power adapter
• DC refill pump
• Universal tube holder
• Siphon break
• Tubing, 200 cm, 6.5 mm internal / 9.0 mm external diameter

Not included

A top-up reservoir is not supplied. AutoAqua's package contents list does not include one, and the manual specifies no reservoir size or material, so the container is your choice.

The sensor magnet and the universal tube holder both clamp through glass or acrylic up to 12.7 mm. Above that thickness the magnets will not hold reliably.

The 180 cm sensor lead sets how far the controller can sit from the sensor, and the 180 cm pump lead sets how far the reservoir can sit from the controller. The pump lifts water 250 cm at zero flow, so a reservoir on the floor of a standard cabinet is well inside range.

One placement rule from the manual: the siphon break must sit higher than the water level in the reservoir, or the tank can siphon itself back down into the container.

• Suitable for freshwater and marine aquariums and sumps, where evaporation is measured in litres a day rather than millilitres.
• Suitable for installations where the controller needs to sit away from the water, on the outside of a cabinet.
• Not suitable for glass or acrylic thicker than 12.7 mm at the sensor or tube holder position.
• Not suitable for a nano tank, where 280 L/h overshoots between readings. The AutoAqua Smart ATO nano G2 meters at 12 L/h for exactly that reason.
• Not suitable for dosing additives. AutoAqua publishes no dosing accuracy for this pump and does not present it as a dosing unit.
• Not suitable for a position where micro-bubbles reach the sensor. The manual warns that bubbles cause false readings.

Mount the dual sensor at your normal water level, with the water reaching the lower detection point. On a small aquarium the upper fail-safe point will trigger after each top-off, and the manual states this is normal.

The mounting magnets are strong enough that AutoAqua prints an injury warning about them. Worth respecting when you are working one-handed inside a cabinet.

Keep the sensor out of direct light and away from anywhere micro-bubbles collect. Both defeat an optical sensor.

Rinse the pump inlet when flow drops off. A fouled inlet is the usual cause of a QST alarm on an otherwise healthy unit. Wipe salt creep and biofilm off the sensor face so the optics stay clear.

Fill the reservoir with water your tank already agrees with. Top-up water is added continuously and never removed, so anything dissolved in it accumulates.

• AutoAqua Smart ATO RO — automates the other half of the job by refilling the reservoir itself from your RO line.
• Reef Pure 4 Stage Essentials+ — an RO/DI unit to make the top-up water the Duo will be moving.
• AutoAqua Smart Level Security — an independent level alarm that cuts power to equipment, sitting outside the Duo's own logic.
• AutoAqua Digital Inline TDS Titanium S1 — shows when the water going into the reservoir has stopped being pure.
• AutoAqua Smart ATO Lite — the same pump and head with a shorter sensor lead, if the controller can sit close to the tank.

AutoAqua's manual states a two-year warranty from the date of purchase, valid through an authorised reseller. That warranty applies in addition to the consumer guarantees you have under Australian Consumer Law, not instead of them.

The adapter accepts 100–240 V AC at 50–60 Hz, so Australian 240 V / 50 Hz mains is within specification. Ships as a standard parcel, with no dangerous goods or oversize handling.

Does the AutoAqua Smart ATO Duo include a top-up reservoir?

No. The AutoAqua Smart ATO Duo ships with the controller and dual optical sensor, a DC pump, a universal tube holder, a siphon break, 200 cm of tubing and a power adapter. You supply the reservoir.

What stops the Smart ATO Duo from overfilling the tank?

Three separate things. The sensor body carries a fail-safe detection point above the ATO level point. The QST timer alarms if a refill runs six times longer than the first refill it learned. And the controller detects an empty reservoir, a failed sensor and a failed pump.

How high can the Smart ATO Duo lift water?

250 cm at zero flow. Flow falls as head rises, so a reservoir on the floor under a cabinet delivers less than the 280 L/h headline, which is measured with no lift at all.

What is the difference between the Smart ATO Duo and the Smart ATO Lite?

Both use the same DC pump, rated 280 L/h and 250 cm of head. The Duo has a 180 cm sensor lead against the Lite's 120 cm, adds a touch button, and its manual specifies an audible and visual alarm where the Lite's manual specifies a visual alert. The Lite's manual states a one-year warranty; the Duo's states two.

Will the Smart ATO Duo work on a rimless tank?

Yes, provided the glass is 12.7 mm or thinner where the sensor magnet and tube holder clamp on. Thicker glass is outside AutoAqua's stated mounting range.

Can I run the Smart ATO Duo on tap water?

Mechanically yes, and AutoAqua publishes no requirement to use RO or RO/DI water. In practice top-up water is added continuously and never removed, so anything dissolved in it concentrates in the tank over time.